1. Field of the Invention
This invention relates generally to data transfer apparatus and, more particularly, is directed to apparatus for transferring data between microcomputer apparatus and a floppy disc controller of a floppy disc system.
2. Description of the Prior Art
Generally, in microcomputer systems, data transfers between an external memory, such as a floppy disc, and a main memory of microcomputer apparatus must pass through the central processing unit (CPU) of the microcomputer apparatus, and therefore, must be implemented in the software of the system. This normally involves the execution of a detailed instruction sequence for inputting, outputting and tracking each byte of data in a block to be transferred, whereby transfer of data occurs one byte at a time. As a result, CPU transfers are relatively slow and tie up the CPU for long periods of time.
Therefore, when using a floppy disc system with microcomputer apparatus, it is desirable to transfer data rapidly between a floppy disc controller of the floppy disc system and the main memory of the microcomputer apparatus. In order to achieve such rapid transfer, direct memory access (DMA) controllers are conventionally used to perform direct transfers of data between the floppy disc controller and the main memory of the microcomputer apparatus, without going through the CPU and without the instruction fetches required by the CPU. In other words, all of the data transfer is performed through hardware of the DMA controller. As a result, DMA transfer of data requires relatively complex circuitry, whereby the entire system becomes rather large and expensive.